Results

Flow of Study Selection and Descriptives

We identified number of records records. See Figure 1 for the PRISMA flow diagram. A total of 11 studies with data from 771 participants were eligible for inclusion.

Figure 1: PRISMA flow diagram

10 of the studies were RCTs, and 1 was a crossover RCT (Greene & Petruzzello, 2022). 8 of the 11 studies were included in the meta-analyses (Bryant et al., 2023; Huseth, 2021; Nordbrandt et al., 2020; Rosenbaum et al., 2015; Voorendonk et al., 2023; Whitworth et al., 2019a; Whitworth et al., 2019b; Young-McCaughan et al., 2022). Meta-analysis was not feasible for 3 of the 11 studies (Crombie et al., 2021a; Greene & Petruzzello, 2022; Powers et al., 2015). These were synthesized descriptively without meta-analysis. Three of the studies provided follow-up PTSD outcome data which were insufficient for synthesis (Bryant et al., 2023; Voorendonk et al., 2023; Young-McCaughan et al., 2022). Three studies examined putative mediators but were only summarised descriptively (Crombie et al., 2021a; Powers et al., 2015; Whitworth et al., 2019b).

Study characteristics of the 8 studies included in the meta-analysis are summarized in Table 1. From these 8 studies, there were 9 eligible comparisons. One study presented findings from two independent comparisons, including a total of four distinct intervention groups (Young-McCaughan et al., 2022). One of the first authors published findings from two different but methodologically similar trials in the same year (Whitworth et al., 2019a; Whitworth et al., 2019b).

Study Year N Intervention Comparison PTSD tool Trial registered Exercise type Exercise intensity Intervention length FU1 FU2 Country
Bryant2023 2023 130 exercise + therapy attention control + therapy CAPS-IV yes aerobic high 10 weeks 34 weeks NA Australia
Voorendonk2023 2023 120 exercise + therapy attention control + therapy PCL-5 yes mixed moderate 12 weeks 26 weeks NA Netherland
Nordbrandt2020 2020 224 exercise + TAU TAU HTQ yes mixed moderate 20 weeks NA NA Denmark
Rosenbaum2014 2014 81 exercise + TAU TAU PCL-4 yes mixed high 12 weeks NA NA Australia
Young-McCaughan2022b 2022 36 exercise + therapy therapy only PCL-5 no aerobic high 8 weeks 12 weeks 32 weeks USA
Huseth2022 2022 21 exercise only WLC PCL-5 no aerobic moderate 8 weeks NA NA USA
Young-McCaughan2022a 2022 36 exercise only TAU PCL-5 no aerobic high 8 weeks 12 weeks 32 weeks USA
Whitworth2019a 2018 30 exercise only attention control PDS-5 no anerobic high 3 weeks NA NA USA
Whitworth2019b 2019 22 exercise only attention control PDS-5 no anerobic high 3 weeks NA NA USA

Aerobic exercise = physical performance behaviour pattern that increases heart rate and respiration while using large muscle groups repetitively and rhythmically; anaerobic exercise = physical performance behaviour pattern that is performed in short intense bursts with limited oxygen intake; mixed exercise = combination of aerobic and anaerobic exercise. CAPS-IV = Clinician-Administered PTSD Scale - 4th edition; PCL-4 = PTSD Checklist - version 4; PCL-5 = PTSD Checklist version 5; HTQ = Harvard Trauma Questionnaire. TAU = treatment as usual.

Table 1: Study characteristics of the 8 studies included in the meta-analysis.

Study characteristics of the 3 studies not included in the meta-analysis are summarized in Table 2. From these 3 studies, there were 4 eligible comparisons.One study reported two comparisons (Greene & Petruzzello, 2022).

Study Year N Intervention Comparison Trial registered Exercise type Exercise intensity Intervention length Country
Crombie2021 2021 38 exercise + extinction learning attention control + extinction learning yes aerobic moderate 3 days USA
Greene2022a 2022 24 exercise only attention control no anaerobic high 130 min USA
Greene2022b 2022 NA exercise only attention control no aerobic  moderate 130 min USA
Powers2015 2015 9 exercise + therapy therapy alone yes aerobic moderate 12 weeks USA

Aerobic exercise = physical performance behaviour pattern that increases heart rate and respiration while using large muscle groups repetitively and rhythmically; anaerobic exercise = physical performance behaviour pattern that is performed in short intense bursts with limited oxygen intake; mixed exercise = combination of aerobic and anaerobic exercise.

Table 2: Study characteristics of the 3 studies not included in the meta-analysis.

The specific intervention and comparison groups for the 11 eligible studies (0 comparisons) are presented in Table 3.

Study Intervention Comparison Exercise type Therapy TAU Attention control
Bryant2023 exercise + therapy attention control + therapy aerobic exposure therapy NA static stretching
Voorendonk2023 exercise + therapy attention control + therapy mixed PE + EMDR NA guided (creative) tasks
Nordbrandt2020 exercise + TAU TAU mixed NA combination: medical doctor, 1 to 2 sessions with social worker / psychologist NA
Rosenbaum2014 exercise + TAU TAU mixed NA combination: individual and group psychotherapy, pharmacotherapy NA
Young-McCaughan2022b exercise + therapy therapy only aerobic imaginal exposure NA NA
Huseth2022 exercise only WLC aerobic NA NA NA
Young-McCaughan2022a exercise only TAU aerobic NA self-care intervention delivering educational and instructional information NA
Whitworth2018 exercise only attention control anaerobic NA NA videos on various educational topics (excluding exercise and mental health).
Whitworth2019 exercise only attention control anaerobic NA NA videos on various educational topics (excluding exercise and mental health).
Crombie2021 exercise + extinction learning attention control + extinction learning aerobic extinction learning NA NA
Greene2022a exercise only attention control mixed NA NA remained sedentary in the lab
Greene2022b exercise only attention control aerobic NA NA remained sedentary in the lab
Powers2015 exercise + therapy therapy alone aerobic prolonged exposure NA NA

Table 3: Specific interventions for all the included studies

Risk of bias assessment

The results of the risk of bias (ROB) assessment per domain and study for the primary outcome, PTSD symptom severity, is presented in Figure 2. Nine studies reported PTSD outcome data post-intervention. Two studies did not report PTSD outcome data (Crombie et al., 2021a; Greene & Petruzzello, 2022). Overall, five studies were rated as high, three studies as some concerns, and one was rated as low risk of bias. High risk of bias was mainly due to deviations from intended intervention (D2)(Voorendonk et al., 2023; Whitworth et al., 2019a; Whitworth et al., 2019b), missing outcome data (D3)(Rosenbaum et al., 2015; Voorendonk et al., 2023; Whitworth et al., 2019a; Whitworth et al., 2019b), and selection of reported results (D5)(Voorendonk et al., 2023; Young-McCaughan et al., 2022).

Figure 2 Risk of bias for PTSD symptom severity

Research question I

Meta-analysis of PTSD Symptom Severity (Primary Outcome)

For the studies included in the meta-analyses, the earliest study was performed in 2014, while the most recent study was performed in 2023. The median sample size across the studies was 36 participants per study. The median of the mean participant age was 37 years (ranging from 29 to 50 years).

8 studies provided data for PTSD symptom severity and contributed 9 effect measures to the PTSD symptom severity meta-analysis. The summary for PTSD symptom severity is shown in Figure 3.

Figure 3: Meta-analysis of the effects of exercise on PTSD symptom severity.

The meta-analysis found no significant difference in PTSD symptom severity between exercise and comparison groups (SMD = -0.08 , 95% CI: -0.24 , 0.07). Low heterogeneity was found as suggested by the prediction interval which is only slightly wider than the confidence interval.

Subgroup Analyses and Meta-regressions

We explored whether heterogeneity could be potentially explained by differences in study-level characteristics using subgroup analyses and meta-regressions. The following characteristics were explored as sources of heterogeneity for the primary outcome, PTSD symptom severity:

  • Exercise intensity (moderate intensity or high intensity)

  • Specific exercise type (aerobic or anaerobic or mixed)

  • Exercise augmented by treatment as usual (TAU)/therapy (exercise only or exercise + therapy/TAU)

  • Intervention length (weeks)

Subgroup analysis by exercise intensity

There was no significant difference in PTSD symptom severity between studies with moderate intensity and those with high intensity exercise groups (Figure 4). However, visual inspection of the forest plot suggests the effect is larger in the high intensity exercise subgroup.

Figure 4: Sub-group analysis of the effects of exercise on PTSD symptom severity by exercise intensity

Subgroup analysis by specific exercise type

The were no significant difference in PTSD symptom severity between studies of aerobic exercise, anaerobic exercise, or mixed (Figure 5).

Figure 5: Sub-group analysis of the effects of exercise on PTSD symptom severity by specific exercise type

Subgroup analysis by exercise alone or tau/therapy augmented by exercise.

There was no significant difference in PTSD symptom severity between studies investigating exercise alone and those investigating TAU/therapy augmented by exercise (Figure 6). However, visual inspection of the forest plot suggests the effect is larger for exercise alone compared with an inactive comparison group than for the studies that augmented psychotherapy and TAU with exercise.

Figure 6: Sub-group analysis of the effects of exercise on PTSD symptom severity by exercise alone or TAU/therapy augmented by exercise

Meta-regression by intervention length

Overall, there is no strong evidence that the intervention length affected the treatment effect. The meta-regression analysis yielded a coefficient of 0.02 (95% CI: -0.01, 0.05).

Figure 7: Meta-regression of the effects of exercise on PTSD symptom severity by intervention length

Meta-analysis of Treatment Dropout (secondary outcome)

8 studies provided data for treatment dropout, and contributed 9 effect measures to the treatment dropout meta-analysis. The forest plot for the risk of treatment dropout is shown in Figure 8.

Figure 8: Meta-analysis of the dropout rates between the intervention and control groups

There is no evidence of a difference in treatment dropout between exercise and comparison groups (RR = 1.28 , 95% CI: 0.67 , 2.45) and there is large heterogeneity, as shown by the prediction interval (0.16 to 10.15).

Sensitivity Analyses

We examine the robustness of the findings for the primary outcome by excluding studies with high risk of bias. 3 studies included in the meta-analyses were rated as low or some concerns. When restricting the analysis to studies with moderate or low risk of bias, the effect of exercise on PTSD symptoms severity is SMD = -0.06 (95% CI: -0.27 , 0.14). For reference, the main effect size for the primary outcome is SMD = -0.08 (95% CI: -0.24 , 0.07), so the results do not change substantially.

Figure 9: Meta-analysis of the effects of exercise on PTSD symptom severity when excluding studies with high risk of bias

Reporting bias

The forest plot below shows the meta-analysis results of the primary outcome ordered by the precision of the studies. It seems that smaller studies showed larger effects favouring the intervention.

Figure 10: Forest plot of the meta-analysis results of the primary outcome ordered by the precision of the studies

Summary of the evidence on the primary outcome from the human studies

The primary outcome was efficacy in reducing overall PTSD symptom severity in patients with PTSD. The summary of the evidence on PTSD symptom severity outcome for PTSD is reported below.

Source of evidence   Summary of the association   Bias due to study limitations Bias due to reporting bias Bias due to indirectedness   Bias due to other reasons
Exercise intervention vs comparison group n = 9 , k = 700 , SMD = -0.08, 95%CI: -0.24, 0.07 Overall, five studies were rated as high, three studies as some concerns, and one was rated as low risk of bias. High risk of bias due to to deviations from intended intervention, missing outcome data, and selection of reported results. Two studies rated as high risk of bias what here Lack of blinding of participants and outcomes assessors.